Embodiments of the invention generally pertain to systems and methods for detecting data on a machine-readable storage medium. In particular, embodiments of the invention pertain to systems and methods for detecting a sync mark for data in a data storage system.
Typically, data is stored on magnetic hard disk drives in concentric tracks on the recording surface or surfaces of the disk or disks. Each track may be divided into a number of addressable sectors, with each sector including a preamble, sync mark, and user data.
The preamble of a disk sector may, for example, contain a pattern of bits that enables the disk read channel to calibrate its gain and allows the read channel to achieve bit synchronization. The preamble may also include a DC erase portion in which there are no logical transitions (e.g., an uninterrupted string of zeros) for a specified length. Since a string of bits with no logical transitions may be illegal everywhere else on the disk, the DC erase portion of the preamble may uniquely identify this portion as being part of the sector preamble.
The sync mark may follow the preamble on a disk sector. In addition, user data may start directly after the last bit of the sync mark. In order to read the user data, it is essential that the sync mark be reliably detected. If the sync mark is not detected, the disk read mechanism may need to re-read the same disk sector for the sync mark. If the disk read mechanism needs to re-read the disk often, the throughput of the disk read channel may suffer, causing a decrease in overall system performance.
Various factors may affect the reliability of sync mark detection in a particular disk sector. For example, as data densities and data rates increase, sources of error in magnetic data storage channels including media noise, electronics and head noise, inter-track interference, thermal asperity, partial erasure, and dropouts, become more pronounced. In addition, the read head may experience a flip in polarity. The flip in polarity may cause the data bits acquired by the read head to be flipped—e.g. a bit containing ‘1’ would be flipped to ‘0’, and vice versa. The polarity of the read head may not be known to the data storage system. Thus, the data storage system may not know when data readout bits acquired by the read head are flipped due to a flip in the polarity of the read head. This lack of knowledge about the polarity of the read head may present a challenge in detecting the sync mark, as the data readout bits may not represent the actual bits written on the disk when the read head is flipped in polarity.
A new sync mark detection scheme is needed to more reliably detect the sync marks of data on disk sectors. Traditional sync mark detection schemes may be inadequate, as they may not take into account the possibility of the polarity flips.
Accordingly, it is desirable to provide systems and methods for sync mark detection taking into account the polarity uncertainty of the disk read head. Further, it is desirable to provide systems and methods for sync mark detection that do not hinder the performance of data storage systems.